The present invention relates to a terminal device adapted to effect transmission and receipt of information through address polling from a central monitoring and control device.
In a monitoring and control system, such as a security system or a burglar system, centralized monitoring and control is generally effected by a central monitoring and control device with respect to various apparatuses to be controlled and/or various sensors such as temperature sensors, smoke density sensors, and burglar sensors that are arranged in various locations within a building. Various terminal devices are provided in correspondence with the various apparatuses and/or sensors, and the central monitoring and control device is adapted to control the various sensors and apparatuses via the terminal devices corresponding to the respective sensors and/or apparatuses.
In such a monitoring and control system, addresses for specifying terminal, devices that communicate with the central monitoring and control device need to be provided in the respective terminal devices themselves. For this reason, each conventional terminal device is provided with a manual switch, such as a multiple switch or a rotary digital code switch, or a semiconductor memory such as a EPROM that has a predetermined number of bits. Addresses peculiar to individual terminal devices are thereby set at the time of manufacture of the terminal devices or when the terminal devices are installed at the installation sites.
With such conventional terminal devices, it is possible to freely set the addresses at the discretion of the operator. However, there is a possibility that the same addresses may be set to a plurality of terminal devices, which can cause abnormalities in transmission. Therefore, when a system includes a multiplicity of terminal devices, it has been necessary to set addresses for the respective terminal devices with the utmost care, so that this setting operation has been time-consuming and has involved much labor.
Where addresses are set in a plurality of terminal devices using the same number of bits (e.g., 20 bits) large enough to overcome the above-described problem and to lower the probability of the addresses of the terminal, devices being duplicated, if the central monitoring and control device polls the terminal devices on the basis of the addresses each having that number of bits, there has been a drawback in that the time duration of transmission with a certain terminal device becomes unnecessarily long, resulting in a decline in transmission efficiency.
To cope with this problem, Japanese Pat. Laid-Open No. 86936/1987 discloses a system in which a plurality of secondary stations are serially connected to each other, and the addresses of the plurality of secondary stations are set automatically in the sequence in which they are connected serially in correspondence with counts of a primary station-side counter. In such a system, it is possible to substantially reduce the time and labor required in setting the addresses of the secondary stations which correspond to the aforementioned terminal devices. In addition, it is possible to prevent errors in a setting process thereof and to prevent a decline in the transmission efficiency.
On the other hand, there are cases where it is desirable for the operator to freely set the addresses at his discretion in such a manner that the probability of the addresses being duplicated is reduced and the efficiency of transmission between the central monitoring and control device and the terminal devices is improved. With the above-described system, however, the addresses are set uniformly in the order of serial connection, and no consideration has been paid to the fact that it is desirable that addresses be set freely irrespective of the state of connection of the terminal devices at the discretion of the operator or the like.